Vesuvianite

Vesuvianite, also called idocrase, is a calcium aluminum sorosilicate mineral first described from Mount Vesuvius. Vesuvianite (also known as idocrase) forms through contact metamorphism when limestone or dolostone is heated by nearby igneous intrusions. The calcium-rich host rock reacts with silicon, aluminum, and other elements from circulating fluids to produce vesuvianite along with other calc-silicate minerals like grossular garnet and diopside.

It was first identified in limestone blocks ejected from Mount Vesuvius, giving it its name. The complex formula reflects its ability to incorporate many different elements, resulting in a wide color range. Green varieties are colored by iron and chromium, brown by iron, and the rare purple cyprine variety contains copper.

Californite is a massive, jade-like variety of vesuvianite found in California that was once marketed as 'California jade.' Transparent, gem-quality crystals suitable for faceting are quite rare and come primarily from Quebec, Kenya, and Pakistan.

Vesuvianite typically forms short prismatic to blocky tetragonal crystals, sometimes with a square cross-section. Green to yellow-green colors, vitreous luster, and hardness of 6.5 are key identifiers. Crystal faces often show vertical striations.

Distinguish from tourmaline (trigonal, no square cross-section), epidote (monoclinic, usually more yellow-green), grossular garnet (isometric, no crystal striations), and zircon (higher specific gravity). Vesuvianite's tetragonal symmetry and association with contact metamorphic rocks help narrow identification.